the scale should have marks that indicate the wavelenghts up to 1 nm. spectral lines of different chemical elements are often very near together, often at a distance of 0,3 nm to 1 nm, so it would be important , if the observed object contains several different elements with very neaerby wavelenghs, that the observer can differentiate betweeen them,. good examles are in the list of spectral-lines in wikipedia, where there are lots of examles for tight wavelenghs of the elements. besides that , one element has mostly several diffrent wavelwenghts in the realm from 400 to 800 nm, so one can terminate and identify it only surely by having more than one wavelenghts of it. so my question aims previously on a mor precise scale.